A machine of the abovementioned kind is known from German specification 41 03 196. In the case of this machine the rotary drive and the impact mechanism are mounted one behind the other in the direction of the axis of the string. For many applications the space requirement that results from this does not play any significant part. It is otherwise, however, if it is desired to start boring from a building or starting trench. When crossing underneath roads the starting trench is often restricted to the breadth of the pavement or else of a front garden. In such tight spaces it is often not possible to use boring machines having the conventional arrangement of the rotary drive arid the impact mechanism.